This International Standard specifies a method for the dissolution of aluminium oxide primarily used for the production of aluminium, by means of attack by hydrochloric acid under pressure in a sealed borosilicate glass tube, in order to obtain a test solution for certain determinations. The method is not applicable to the preparation of test solutions for the determination of silicon, sodium or boron, owing to the possibility of extraction of these elements from the glass. NOTE — Hydrochloric acid may be replaced by another appropriate acid. In this case, the acid should be stated in the method of test of the impurity.